2009-09-21
IEEE 802.16m-09/2193
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Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Proposed Changes/Refinements to Section 10.3 (Handover) in the IEEE 802.16m SDD (802.16m09/0034r1)
Date
Submitted
2009-09-21
Source(s)
Roshni Srinivasan, Reza Arefi, Xiangying Yang
Intel Corporation
Re:
Change Request - 802.16m SDD, IEEE 802.16m-09/0034r1
Abstract
This contribution proposes text changes to the handover section in the 802.16m SDD, IEEE 802.16m09/0034 r1
Purpose
To be discussed and adopted by TGm for the 802.16m SDD
Notice
Release
Patent Policy
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roshni.m.srinivasan@intel.com
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Introduction
This contribution proposes text changes to the handover section in the 802.16m SDD, IEEE 802.16m-09/0034 r1
It is proposed that the resolutions to comment #1629 and #1630 in IEEE 802.16m-09/0047r4 be implemented in the
802.16m SDD for consistency.
___________________________Begin Proposed Text Changes________________________________
10.3
Handover
The following 4 cases are considered for handover in IEEE 802.16m:
Case-1: AMS handover from serving YBS WirelessMAN-OFDMA BS to target YBS WirelessMAN-OFDMA BS
Case-2: AMS handover from serving ABS to target YBS WirelessMAN-OFDMA BS
Case-3: AMS handover from serving YBS WirelessMAN-OFDMA BS to target ABS
Case-4: AMS handover from serving ABS to target ABS
The IEEE 802.16m network and mobile station AMS use legacy handover procedures for case-1.
Solutions for cases 2, 3 and 4 are described in Sections 10.3.3.3, 10.3.3.2 and 10.3.2 respectively.
10.3.1
Network Topology Acquisition
10.3.1.1 Network Topology Advertisement
An ABS periodically broadcasts the system information of corresponding to the neighboring ABSs and/or YBS
WirelessMAN-OFDMA BS using a Neighbor Advertisement message. The ABS formats the Neighbor
Advertisement message based on the cell types of neighbor cells in order to achieve overhead reduction and
facilitate scanning priority for AMS. A broadcast Neighbor Advertisement message does not include information of
neighbor CSG femtocells. Special handling of neighbor information of femtocell BS is described in Section Error!
Reference source not found..
A serving ABS may unicast the Neighbor Advertisement message to an AMS. The Neighbor Advertisement
message may include parameters required for cell selection e.g., cell load and cell type.
10.3.1.2 Scanning Procedure
The scanning procedure provides the opportunity for the AMS to perform measurement of the neighboring cells for
handover decision. The AMS may use any interval not allocated by the serving ABS to perform autonomous
scanning. In addition, the AMS may perform scanning procedure without interrupting its communication with the
serving ABS if the AMS supports such capability.
The AMS selects the scanning candidate ABSs by information obtained from the ABS or information cached in the
AMS. The ABS or AMS may prioritize the neighbor ABSs to be scanned based on various metrics, such as cell
type, loading, RSSI and location.
As part of the scanning procedure, the AMS measures the selected scanning candidate ABSs and reports the
measurement result back to the serving ABS. The measurements may be used by the AMS or the network to
determine the correct target –ABS for the AMS to handover to. The measurements in the Advanced WirelessMANOFDMA Interface include the measurements specified as part of the WirelessMAN-OFDMA Reference system as
well as any other measurements defined in the Advanced WirelessMAN-OFDMA Interface. The serving ABS
defines triggering conditions and rules for AMS sending scanning report.
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10.3.2
Handover Process
10.3.2.1 HO Framework
The handover procedure may be initiated by either the AMS or the ABS. In the case of the AMS initiated HO, the
AMS sends an HO initiation message to the serving ABS (S-ABS). The S-ABS responds to the HO initiation
message by sending an HO command message to the AMS. In the case of the S-ABS initiated HO, the S-ABS sends
an HO Command control message to the AMS. In both cases (HO initiated by AMS or S-ABS) the HO command
message should include one or more target ABSs (T-ABSs). If the HO command message includes only one target
ABS, the AMS should execute the HO as directed by the ABS. An AMS may send a HO indication message to the
S-ABS before the expiration of disconnect time. The S-ABS stops sending DL data and providing UL allocations to
the AMS after expiration of the disconnect time or after reception of HO-IND.
If the HO command message includes more than one target ABSs, the AMS selects one of these targets and informs
the S-ABS of its selection by sending an HO indication message to the S-ABS before the expiration of disconnect
time.
The network re-entry procedure with the target ABS may be optimized by target ABS possession of AMS
information obtained from serving ABS over the backbone network. The AMS may also maintain communication
with serving ABS while performing network re-entry at target ABS as directed by serving ABS. Figure 1 shows a
general call flow for handover.
The S-ABS defines error conditions based on which the AMS decides when a T-ABS among those that are included
in HO command control signaling is unreachable. If all the target ABSs that are included in the HO command
signaling are unreachable, the AMS signals the new T-ABS to the S-ABS by sending HO indication control
signaling before the expiration of disconnect time, and the AMS performs network re-entry at the new T-ABS as
indicated in the HO indication control signaling. The AMS also indicates the identity of its old S-ABS to the new TABS during network entry at the new T-ABS.
Serving
BS
MS
Target
BS
HO Initiation
HO REQ
HO RSP
HO Command
HO Indication
Network re-entry
MS-BS Communication
during Network re-entry
HO CMPLT
Data path established
Figure 1: The general call flow for handover
The handover procedures are divided into three phases, namely, HO initiation, HO preparation and HO execution.
When HO execution is complete, the AMS is ready to perform Network re-entry procedures at target ABS. In
addition, HO cancellation procedure is defined to allow AMS cancel a HO procedure.
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10.3.2.2
HO Procedure
10.3.2.2.1 HO initiation
Handover procedure may be initiated by either the AMS or the ABS. When handover is initiated by the AMS, it is
based on the triggers and conditions defined by the S-ABS. The HO trigger may consist of a combination of
multiple conditions. When HO is initiated by the AMS, a HO Initiation control signaling is sent by the AMS to start
the HO procedure. In case of ABS initiated HO, HO initiation and HO preparation phases are carried out together.
10.3.2.2.2 HO Preparation
During the HO preparation phase, the serving ABS communicates with target ABS(s) selected for HO. The target
ABS may obtain AMS information from the serving ABS via backbone network for HO optimization. If ranging
with target ABS is not performed prior to or during HO preparation, dedicated ranging resource (e.g. code, channel,
etc.) at the target ABS may be reserved for the AMS to facilitate non-contention-based HO ranging. Information
regarding AMS identity (e.g. TEK, STID, FIDs, etc.), may be pre-updated during HO preparation. Any mismatched
system information between AMS and the target ABS, if detected, may be provided to the AMS by the Serving ABS
during HO preparation.
When only one target ABS is included in the HO Command control signaling, the HO preparation phase completes
when serving the ABS informs the AMS of its handover decision via a HO Command control signaling. When
multiple target ABSs are included in the HO Command control signaling, the HO preparation phase completes when
the AMS informs the ABS of its target ABS selection via HO indication control signaling. The HO Command
control signaling may include dedicated ranging resource allocation and resource pre-allocations for the AMS at
each target ABS for optimized network re-entry. The HO Command control signaling includes an action time for the
AMS to start network re-entry at each target ABS and an indication whether the AMS should maintain
communication with serving ABS during network re-entry. The HO Command control signaling further includes a
disconnect time, which indicates when the serving ABS will stop sending downlink data and stop providing any
regularly scheduled unsolicited uplink allocations for the AMS. In the case that AMS maintains communication with
serving ABS during network re-entry, the parameters associated with the scheme of multiplexing transmission with
serving and target ABS are determined by serving ABS based on the AMS capability and negotiated between the
serving and target ABSs.
The HO command control signaling indicates if the static and/or dynamic context and its components of the AMS is
available at the target ABS.
10.3.2.2.3 HO Execution
At the action time specified in the HO command control signaling, the AMS performs network re-entry at the target
ABS. If communication is not maintained between the AMS and the serving ABS during network re-entry at the
target ABS, the serving ABS stops allocating resources to the AMS for transmission at disconnect time.
If directed by serving ABS via HO Command control signaling, the AMS performs network re-entry with the target
ABS at action time while continuously communicating with the serving ABS. However, the AMS stops
communication with serving ABS after network re-entry at the target ABS is completed. In addition, the AMS
cannot exchange data with target ABS prior to completion of network re-entry. Multiplexing of network re-entry
signaling with the target ABS and data communications with the serving ABS is done by negotiating with the
serving ABS for some intervals for network re-entry signaling with the target ABS, and the remaining intervals for
data communication with the serving ABS. If the negotiated interval is set to 0, the AMS communicates with the
serving ABS continuously while concurrently performing network re-entry with the target ABS. In case of single
radio AMSs, the negotiated interval excludes the value 0.
10.3.2.2.4 HO Cancellation
After HO is initiated, the handover may be canceled by the AMS at any phase during HO procedure. After the HO
cancellation is processed, the AMS and the serving ABS resume their normal operation.
The network can advertise HO cancellation trigger conditions. When one or more of these trigger conditions are met
the AMS cancels the HO.
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10.3.2.3 Network Re-entry
The network re-entry procedure is performed as specified in the WirelessMAN OFDMA Reference System unless
otherwise specified in this section.
If a dedicated ranging code is assigned to the AMS by target ABS, the AMS transmits the dedicated ranging code to
the target ABS during network re-entry. If a ranging channel is scheduled by the target ABS for handover purpose
only, the AMS should use that ranging channel in order to avoid excessive multiple access interference. Upon
reception of the dedicated ranging code, the target ABS should allocate uplink resources for AMS to send RNGREQ message and UL data if needed.
When the AMS performs handover to the target ABS, CDMA-based HO ranging may be omitted.
10.3.3
Handover Process Supporting WirelessMAN OFDMA Reference System
The text in this subclause summarizes handover involving a WirelessMAN-OFDMA Advanced System and a
WirelessMAN-OFDMA Reference System specified per subclause 12.5 of IEEE Std 802.16-2009 [3]. Handover
involving an WirelessMAN-OFDMA Advanced System and an FDD system covered under subclause 12.7 of IEEE
Std 802.16-2009 [3] follows similar procedures.
10.3.3.1
Network Topology Acquisition
The When a WirelessMAN-OFDMA Reference System /- co-exists with a WirelessMAN-OFDMA Advanced
System, co-existing system consists of WirelessMAN-OFDMA Reference System and WirelessMAN-OFDMA
Advanced System, cells/sectors may belong to either system. An YBS WirelessMAN-OFDMA BS advertises the
system information for corresponding to its neighbor YBS WirelessMAN-OFDMA BSs and the LZones of its
neighbor ABSs. An ABS advertises the system information for its neighbor YBS WirelessMAN-OFDMA BSs in its
both LZone and MZone. It advertises the LZone system information of its neighbor ABSs in its LZone. It also
advertises the system information for corresponding to its neighbor ABSs in its MZone.
The ABS may indicate its WirelessMAN-OFDMA Advanced capability and information in its LZone broadcast
information (e.g. by the modified reserved bit of the FCH and the MAC version TLV).
10.3.3.2
Handover from YBS WirelessMAN-OFDMA BS to ABS
When a handover from a WirelessMAN-OFDMA Reference System to a WirelessMAN-OFDMA Advanced System
is triggered for a YMS WirelessMAN-OFDMA MS, the YMS WirelessMAN-OFDMA MS handover is from the
serving YBS WirelessMAN-OFDMA BS to the LZone of the target ABS using WirelessMAN-OFDMA Reference
System handover signaling and procedures.
An AMS may handover from the serving YBS WirelessMAN-OFDMA BS to the LZone of the target ABS using a
WirelessMAN-OFDMA Reference System handover signaling and procedures, and switch to the MZone of the ABS
after AMS entering LZone. The detailed procedure for zone switching is FFS.
An AMS may also handover from a YBS WirelessMAN-OFDMA BS to a WirelessMAN-OFDMA-AdvancedSystem-only ABS or MZone of ABS directly if AMS is able to scan WirelessMAN-OFDMA-Advanced-Systemonly ABS or MZone prior to handover. The detailed procedure is FFS.
10.3.3.3
Handover from ABS to YBS WirelessMAN -OFDMA BS
When a handover from the WirelessMAN-OFDMA Advanced System to the WirelessMAN-OFDMA Reference
System is triggered for a YMS WirelessMAN-OFDMA MS, the YMS WirelessMAN-OFDMA MS handover is
from LZone of the serving ABS to the target YBS WirelessMAN-OFDMA BS using handover signaling and
procedures as defined in WirelessMAN-OFDMA Reference System.
When a handover from the WirelessMAN-OFDMA Advanced System to the WirelessMAN-OFDMA Reference
System is triggered for an AMS, the serving ABS and AMS perform handover execution using handover signaling
and procedures as defined in the WirelessMAN-OFDMA Advanced System. The serving ABS performs context
mapping and protocol inter-working from the WirelessMAN-OFDMA Advanced System to the WirelessMAN-
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OFDMA Reference System. Then the AMS perform network re-entry to target YBS WirelessMAN-OFDMA BS
using network re-entry signaling and procedures as defined in the WirelessMAN-OFDMA Reference System.
10.3.4
Inter-RAT Handover Procedure
10.3.4.1 Network Topology Acquisition
IEEE 802.16m systems advertise information about other RATs to assist the AMS with network discovery and
selection. IEEE 802.16m systems provide a mechanism for AMS to obtain information about other access networks
in the vicinity of the AMS from a ABS either by making a query or listening to system information broadcast. This
mechanism can be used both before and after AMS authentication. IEEE 802.16m system may obtain the other
access network information from an information server. The ABSs may indicate the boundary area of the IEEE
802.16m network by advertising a network boundary indication. Upon receiving the indication, the AMS may
perform channel measurement to the non-IEEE 802.16m network.
10.3.4.2 Generic Inter-RAT HO procedure
IEEE 802.16m system provides mechanisms for conducting inter-RAT measurements and reporting. Further, IEEE
802.16m system forwards handover related messages with other access technologies such as IEEE 802.11, 3GPP
and 3GPP2. The specifics of these handover messages may be defined elsewhere, e.g. IEEE 802.21.
10.3.4.3
Enhanced Inter-RAT HO procedure
10.3.4.3.1 Dual Transmitter/Dual Receiver Support
In addition to the HO procedures specified in Section 10.3.4.2, an AMS with dual RF may connect to both an ABS
and a BS operating on other RAT simultaneously during handover. The second RF is enabled when inter-RAT
handover is initiated. The network entry and connection setup processes with the target BS are all conducted over
the secondary radio interface. The connection with the serving BS is kept alive until handover completes.
10.3.4.3.2 Single Transmitter/Single Receiver Support
An AMS with a single RF may connect to only one RAT at a time. The AMS will use the source RAT to prepare the
target RAT system. Once target RAT preparation is complete the AMS may switch from source RF to target RF and
complete network entry in target RAT. Only one RF is active at any time during the handover.
___________________________End Proposed Text Changes________________________________
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